Manufacture of webs having selected oriented portions

ABSTRACT

Manufacture of a thermoplastic polymeric web or film having a predetermined pattern of molecularly oriented portions by completely cooling an extruded flat unbroken steam of molten orientable crystallizable, thermoplastic polymeric material to provide an integral web, with selected spaced areas of such stream being cooled more slowly than the regions adjacent thereto, and thereafter stretching the web along biaxial directions.

United States Patent Fairbanks [4 1 Sept. 26, 1972 [s41 MANUFACTURE OFWEBS HAVING 3,423,274 1/1969 Lahm et a1 ..264/348 SELECTED ORIENTEDPORTIONS' 3,386,376 6/1968 [72] inventor: Theodore H Fairbanks, RD. 13,255,065 6/1966 \Yyckoff ..264/289 Liverpool 1.17045 ,500,627 3/1970K|m.. ..264/DIG. 47 I p 2,952,878 9/1960 Swerhck et a1. ..264/289 [731 VAssignee: FMC Corporation, Philadelphia, Pa. P E R b F wh rzmaryxaminero ert rte [22] Ffled Sept 1970 Assistant Examiner-Jeffery R.ThurIow [21] Appl. No; 73,435 Attorney-Thomas R. OMalley, George F.Muelle and Eugene G. Horsky Related US. Application Data I [63]Continuation-impart of Ser. No. 784,383, Dec. [57] ABSTRACT 1968,Manufacture of a thermoplastic polymeric web or film having apredetermined pattern of molecularly US. 5 264/210 oriented portions bycompletely cooling an extruded 264/237, 264/28 4/348, 264/DlG- 47 flatunbroken steam of molten orientable crystalliza Int. Cl. ..B29c 25/0329d 329d ble, thermoplastic polymeric material to provide an in- [58]Field of Search ..264/ 167, 147, 177, 145, 348, tegral web, withselected spaced areas of such stream 264/154, 210 R, 289, 237, D10. 47being cooled more slowly than the regions adjacent thereto, andthereafter stretching the web along biaxi- [56] References Cited aldirections. I

UNITED STATES PATENTS S-Ciaims, 5 Drawing Figures 3,137,746 6/1964Seymour et a1, ..264/289 LONGITUDINAL STRETCH T R A N S V E R S E ST R ET C H 45 MANUFACTURE OF WEBS HAVING SELECTED ORIENTED PORTIONS Thisapplication is a continuation-in-part of my application Ser. No.784,383, filed Dec. 17, 1968, now US. Pat. No. 3,632,716.

The present invention is directed to an improved method for making filmsor webs from thermoplastic polymeric materials which possess highstrength, stiffness and tear resistant properties.

US. Pat. No. 3,255,065, issued on June 7, 1966, to H. Wyckoff, disclosesa method and apparatus for making a composite film by laminating, orotherwise uniting, an unbroken and unoriented web of ther moplasticpolymeric material with a similar web having a series of openings orperforations disposed in a predetermined pattern, followed by astretching of the laminated structure along desired directions.

Upon stretching of such laminated structure along its longitudinal andtransverse axes, the portions of the unbroken web which extend acrossthe openings in the perforated web are biaxially oriented. The ribs ofthe perforated web, and the portions of the unbroken web attachedthereto, are uniaxially oriented and impart desired stiffness into theresulting composite film, while the areas of the laminated structurewhich are located betweenthe ends of such ribs remain undrawn.

As more fully described in the above-noted patent, the relationshipbetween the spacing and size and/or shape of the openings in theperforated web is of critical importance from the standpoint ofisolating the effects of the stretching forces to the ribs themselves sothat undrawn junctions remain between the uniaxially drawn ribs.

The manufacture of composite films by the method described in thevabove-noted patent requires the production of separate unoriented websof thermoplastic polymeric material, the perforating of one of suchwebs, the laminating of the unperforated and perforated webs, andfinally the biaxial stretching of the laminated structure. Thesenumerous manipulative steps, taken with the critical care which must beexercised to insure proper web perforation and lamination render theabove-described patented method slow and costly.

A primary object of this invention is to provide a new or generallyimproved and more satisfactory method for making a thermoplasticpolymeric web or film having good strength and stiffness along itsselected directions and which exhibits improved tear resistantcharacteristics.

Another object is the provision of a method for providing a web ofthermoplastic polymeric material of generally uniform thickness with apredetermined pattern of molecularly oriented portions.

Still another object of this invention is a method which is adapted forrapid and economical manufacture of thermoplastic polymeric webs orfilms having a predetermined pattern of molecularly oriented portions.

A further object is the provision of a method for making a thermoplasticpolymeric film having fabriclike properties along selected portionsthereof.

For a greater understanding of this invention, reference is made tothefollowing detailed description and drawing in which FIG. 1 is adiagrammatic view of apparatus employed in the method of the presentinvention;

FIG. 2 is a front view of a chill roller employed in the apparatus shownin FIG. 1;

FIG. 3 is a plan view of a portion of a thermoplastic polymeric webproduced on the chill roller shown in FIGS. 1 and 2;

FIG. 4 is a plan view illustrating the web of FIG. 3 after it has beenstretched along one of its axial directions; and

FIG. 5 is a plan view illustrating the web shown in FIG. 4, on a smallerscale, after it has been stretched along another of its biaxialdirections.

The above and other objects of the invention are achieved by a method inwhich an extruded flat and unbroken stream of molten thermoplasticpolymeric material is cooled to provide an integral web, with selected,independent and substantially like areas, aligned longitudinally andtransversely of the extruded stream and equally spaced in theirrespective directions, being cooled at a slower rate than the re gionswhich are adjacent thereto. The regions of the ex truded stream whichare adjacent to the selected areas thereof are cooled at a rate as to atleast minimize and preferably prevent crystal formation therein. Oncecooled, the web is stretched along biaxial directions whereby theregions between adjacent transversely aligned selected areas areuniaxially oriented in a direction transversely of the web, while theregions between adjacent longitudinally aligned selected areas are alsouniaxially oriented but in a direction longitudinally of the web. Theselected areas of the web remain substantially undrawn while theremaining regions of the web are biaxially oriented.

The method of the present invention is adapted for use with orientable,crystallizable thermoplastic polymeric materials. As described above,the extruded stream of molten thermoplastic polymeric material iscompletely cooled after its extrusion and before stretching, with theselected areas thereof being cooled at a slower rate than the regionswhich are adjacent thereto. Crystallization accompanies this slowercooling in the selected areas of the web and thus such selected areasundergo no apparent or significant drawing during the subsequentstretching stage.

In the practice of the method of the present invention, the web may bestretched along biaxial directions in independent steps orsimultaneously. The degree to which the web is stretched in either ofits biaxial directions may be varied and is preferably such as to orientall regions between the transversely and longitudinally aligned selectedareas of the web. Fabric-like characteristics may be imparted to theresulting product by exerting such stretching as to cause fibrillationof the biaxially oriented regions thereof. Heat may be applied to theweb which is being stretched prior to and/or during the actualstretching step to encourage the drawing thereof.

In general, the apparatus employed in the method of the presentinvention includes means for extruding a continuous, flat and unbrokenstream of molten thermoplastic polymeric material, a patterned chillmember positioned to receive upon its surface the flat stream of moltenthermoplastic material as it issues from the extruding means for coolingthe same into an integral web, means for moving the chill memberrelative to the extruding means, and means for stretching the web alongbiaxial directions. The chill member is preferably a roller having apatterned peripheral surface in which selected surface areas thereof aredefined by like, spaced depressions. Preferably, these depressions areof circular and concave configuration.

The method of the present invention is adapted for use in making filmsfrom all crystallizable thermoplastic materials, the molecules of whichmay be oriented by stretching. The particular polymeric materialemployed will, in general, depend upon the intended use of the resultingproduct. The products made in accordance with the teachings of thepresent invention are suited for a variety of uses in which either thenon-porous or the fabric-like properties of the product are ofparticular importance and where high strength, stiffness and tearresistance are desired characteristics. For example, webs made by thepresent invention may be used as protective coverings or shields as inbuilding construction, as article wrapping or bagging materials, asinflatable structures, such as observation balloons, life rafts, etc.

For a more detailed description of the method of the present invention,reference is made to FIG. 1 of the drawing wherein character denotes aportion of a die or nozzle, which is part of a conventional extrusionsystem, from which a flat unbroken stream 17 of molten thermoplasticpolymeric material, such as polyethylene terephthalate is extruded. Thisextruded stream 17 of molten thermoplastic polymeric material isreceived upon a chill roller 19 which, as shown in FIG. 2, is formedwith depressions 21 in its peripheral surface. These depressions 21 areof substantially like circular and concave configuration, and arealigned longitudinally and circumferentially of the roller surface andare equally spaced along their respective longitudinal andcircumferential directions. Suitable means, not shown, is provided forcontinuously driving the roller 19 in the direction as indicated byarrow 23. The roller 19 is cooled by circulating a chilled liquidtherethrough or by any other known and conventional manner.

The stream 17 of molten thermoplastic material extruded from the nozzle15 is received upon the chill roller 19 where it spans the depressions21 while making snug contact with the remaining portions of the chillroller surface. While engaged and traveling with the chill roller 19 thestream 17 is quenched to provide an integral web 25.

During quenching, the areas of the stream 17 overlying the chill rollerdepressions 21 are, of course, cooled at a slower rate than the regionsadjacent thereto which are in direct and snug contact with the surfaceof the roller 19. As a result, crystallization takes place in theseslower cooling areas of the stream 17 during its quenching and, in theweb 25, such areas have been identified at 27.

The rate of cooling and thus the degree of crystallini ty which occursin the selected areas 27 of the web 25, will depend upon such factors asthe temperatures of the chill roller 19, the ambient atmosphere andextruded molten thermoplastic material and the size, depth and spacingof the chill roll depressions or indentations 21, and thus can be variedto provide for desired properties in the finished product. The web 25 ispreferably completely cooled on the chill roller 19.

The web 25 is removed from the surface of the chill roller 19 by astripping roll 29 and is passed in-between pairs of conventional drivennip rolls 31 and 33. The nip rolls 33 are driven at a more rapid ratethan the nip rolls 31 whereby sections 35, which extend transversely ofthe web at longitudinally spaced intervals thereof, are stretchedlongitudinally to orient the molecules thereof, as indicated by shadingin FIG. 4. The crystallization which has occurred in the areas 27prevent these areas as well as the regions extending transverselybetween adjacent of such areas, from yielding under the longitudinalstretching forces.

Once beyond the nip rolls 33, the web 25 is passed into a conventionaltenter frame 37 where its longitudinal edges are gripped at spacedintervals by clips 39 carried by endless belts 41. From the nip rolls33, the belts 41 of the tenter frame 37 are directed along divergingpaths. Thus, during movement with the tenter frame belts 41 sections 43of the web 25, which extend longitudinally of the web at transverselyspaced intervals thereof, are stretched to orient the molecules thereofas indicated by shading in FIG. 5. As during the longitudinal stretchingof the web 25, the crystalline areas 27 do not yield during thisstretching stage and thus prevent transverse drawing of the regions ofthe web located between the adjacent longitudinally aligned areas 27.

The web 25 may be heated to a desired orientation temperature rangeduring the stretching thereof and, once stretched, the web 25 isreleased from the tenter frame, cooled if necessary, and advanced by niprolls 45 to a suitable collection means, not shown.

In the resulting web product, as shown in FIG. 5, the selected areas 27are, of course, undrawn, while ribs 47 between longitudinally alignedareas 27 and ribs 49 between transversely aligned areas 27 have beenuniaxially stretched and thus oriented in the directions as indicated bydouble-headed arrows in the respective ribs. The remaining regions 51 ofthe web 25 have been subjected to both longitudinal and transversestretching forces, as indicated by crossing arrows, and thus themolecules thereof have been biaxially oriented.

The uniaxially oriented webs 47 and 49 impart stiffness into the web 25in the respective directions of such ribs and, together with thebiaxially oriented regions 51, improve the web tensile strengthproperties. The unoriented areas 27 are well isolated from each other bythe surrounding oriented ribs 47 and 49 and serve well in arresting anytearing which may initiate at other regions of the web.

While the size, shape and/or configuration of these selected unorientedareas 27 formed in the unoriented web 25 may be varied to provide in theresulting stretched product desired stiffness and/or strengthcharacteristics, such areas 27 must be of substantially like size,aligned longitudinally and transversely of the web, and equally spacedin their respective longitudinal and transverse directions.

I claim:

1. A method of making a web of polymeric material having a predeterminedpattern of molecularly oriented portions including the steps ofextruding a flat, unbroken molten stream of orientable, crystallizable,thermoplastic polymeric material, completely cooling the extruded streamof molten thermoplastic material biaxial directions to'cause regions ofthe web between adjacent transversely aligned selected areas to beuniaxially oriented in a direction transversely of the web, regions ofthe web between adjacent longitudinally aligned selected areas to beuniaxially oriented in a direction longitudinally of the web, theselected areas themselves to be substantially undrawn and the remainingregions of the web to be biaxially oriented.

2. A method as defined in claim 1 wherein the regions of the extrudedstream of polymeric material which are adjacent to the selected areasthereof are cooled at a rate as to at least minimize crystallizationthereof.

3. A method as defined in claim 2 wherein the regions of the extrudedstream of polymeric material which are adjacent to the selected areasthereof are cooled at a rate as to prevent crystal fonnation thereon.

4. A method as defined in claim 1 wherein the web is stretched toproduce fibrillation along the biaxially oriented regions thereof.

5. A method as defined in claim 1 wherein the web is stretchedsimultaneously along biaxial directions.

1. A method of making a web of polymeric material having a predeterminedpattern of molecularly oriented portions including the steps ofextruding a flat, unbroken molten stream of orientable, crystallizable,thermoplastic polymeric material, completely cooling the extruded streamof molten thermoplastic material to provide an integral web withselected, independent and substantially like areas alignedlongitudinally and transversely of the extruded stream and equallyspaced from each other in their respective directions, being cooled at aslower rate than the regions adjacent thereto to thereby impart a higherdegree of crystallinity to such selected areas, and stretching the webalong biaxial directions to cause regions of the web between adjacenttransversely aligned selected areas to be uniaxially oriented in adirection transversely of the web, regions of the web between adjacentlongitudinally aligned selected areas to be uniaxially oriented in adirection longitudinally of the web, the selected areas themselves to besubstantially undrawn and the remaining regions of the web to bebiaxially oriented.
 2. A method as defined in claim 1 wherein theregions of the extruded stream of polymeric material which are adjacentto the selected areas thereof are cooled at a rate as to at leastminimize crystallization thereof.
 3. A method as defined in claim 2wherein the regions of the extruded stream of polymeric material whichare adjacent to the selected areas thereof are cooled at a rate as toprevent crystal formation thereon.
 4. A method as defined in claim 1wherein the web is stretched to produce fibrillation along the biaxiallyoriented regions thereof.
 5. A method as defined in claim 1 wherein theweb is stretched simultaneously along biaxial directions.